目的·评估0.5 s用力呼气容积（forced expiratory volume in 0.5 second，FEV_0.5）与FEV_0.75在肺通气功能检查中实测值/预测值的异常率，以及在支气管舒张试验前后改善率的不同截止点在支气管哮喘（哮喘）患儿诊断中的临床意义。方法·选择2020年1月—2021年2月在浙江大学医学院附属儿童医院住院期间被诊断为哮喘的学龄期患儿为对象。收集患儿的肺通气功能检查及支气管舒张试验检测的数据资料。比较患儿在肺通气功能检查中FEV_t实测值/预测值的异常率差异。采用诊断试验四格表分析支气管舒张试验前后FEV_0.5改善率和FEV_0.75改善率的不同截止点对哮喘诊断的灵敏度和特异度。结果·共计纳入148例患儿。所有入组病例均完成了肺通气功能检查，其中51例同时完成了支气管舒张试验。肺通气功能检查的结果显示，21例患儿为阻塞性通气功能障碍，30例患儿为小气道功能障碍，其余患儿为正常、存在限制性通气功能障碍或混合型通气功能障碍。支气管舒张试验检测的结果显示，在51例阻塞性通气功能障碍和小气道功能障碍的哮喘患儿中，有22例为支气管舒张试验阳性。FEV_t实测值/预测值的异常率比较的结果显示，FEV_0.75实测值/预测值的异常率高于FEV₁、FEV_0.5的异常率（χ²=10.18，P=0.000；χ²=10.95，P=0.000）。EFV_0.75和FEV_0.5改善率的不同截止点的灵敏度及特异度分析的结果显示，FEV_0.5改善率的截止点选取16%时具有非常高的灵敏度及特异度，约登指数最高；FEV_0.75改善率的截止点选取12%和14%的灵敏度及特异度均达到100%。结论·肺通气功能检查中FEV_0.75实测值/预测值可考虑作为FEV₁实测值/预测值的替代指标，对是否存在阻塞性通气功能障碍行进一步评估。在支气管舒张试验结果的基础上，可考虑结合FEV_0.75与FEV_0.5改善率的最佳截止点对气道可逆性进行分析，以提高支气管舒张试验对哮喘诊断的临床价值。

Objective ·To evaluate the abnormal rates of measured/predicted values of forced expiratory volume in 0.5 second (FEV_0.5) and FEV_0.75 in lung ventilation function testing, as well as the clinical significance of different cut-off points for improvement rates before and after bronchodilation testing in the diagnosis of children with bronchial asthma (asthma). Methods ·From January 2020 to February 2021, school-age children diagnosed with asthma during their hospitalization at the Children's Hospital, Zhejiang University School of Medicine were selected. The data on lung ventilation function testing and bronchodilator testing were collected. The difference in abnormal rates of measured/predicted values of FEV_t in children in lung ventilation function testing was compared. Diagnostic test four grid table was used to analyze the sensitivity and specificity of different cut-off points for the improvement rates of FEV_0.5 and FEV_0.75 in the diagnosis of asthma before and after bronchodilation testing. Results ·A total of 148 children were included. All enrolled cases completed lung ventilation function testing, with 51 cases completing bronchodilation testing simultaneously. The results of lung ventilation function testing showed that 21 patients had obstructive ventilation dysfunction, 30 patients had small airway dysfunction, and the remaining patients had normal, restrictive or mixed ventilation dysfunction. The results of bronchodilation testing showed that in the 51 asthmatic children with obstructive ventilation dysfunction and small airway dysfunction, 22 of them were positive for bronchodilation testing. The comparison of the abnormal rates of FEV_t measured/predicted values showed that the abnormal rates of FEV_0.75 measured/predicted values were higher than those of FEV₁ and FEV_0.5 (χ²=10.18, P=0.000; χ²=10.95, P=0.000). The sensitivity and specificity analysis results of different cut-off points for the improvement rates of EFV_0.75 and FEV_0.5 showed that the cut-off point for FEV_0.5 improvement rate at 16% had very high sensitivity and specificity, with the highest Jordan index; the cut-off points for FEV_0.75 improvement rate were 12% and 14%, respectively, with sensitivity and specificity reaching 100%. Conclusion ·The measured/predicted value of FEV_0.75 in lung ventilation function testing can be considered as an alternative indicator for the measured/predicted value of FEV₁ to further evaluate the presence of obstructive ventilation dysfunction. On the basis of the results of bronchodilation testing, it can be considered to analyze the airway reversibility by combining the best cut-off points of FEV_0.75 and FEV_0.5 improvement rates, in order to enhance the clinical value of bronchodilation testing in the diagnosis of asthma.